I've looked around gamedev some and it seems like there's a really supportive community, so I decided to try getting support on this error I'm getting.

I'm learning C++ from a book; I'm just beginning in it, so this is a really simple program. The idea is: the user enters a number, which the computer guesses at. However, in the section where I'm modifying the ai's guessing logic, I'm getting an error I can't find a good way to get around. I included a picture of the code and error. When I hover my mouse over the variables "guess" in the arithmetic within the 'if' blocks, it says: "Error: Expression must be a modifiable lvalue"

I would really appreciate an explanation of what that means and maybe a suggestion to fix it.